Described herein are a soybean gene for resistance to Aphis glycines, soybean plants possessing this gene, which maps to a novel chromosomal locus, and methods for identifying and breeding these plants, the methods involving marker-assisted selection.
Soybeans (Glycine max L. Merr.) are a major cash crop and investment commodity in North America and elsewhere. Soybean oil is one of the most widely used edible oils, and soybeans are used worldwide both in animal feed and in human food production.
A native of Asia, the soybean aphid was first found in the Midwest in 2000 (Hartman, G. L. et al., “Occurrence and distribution of Aphis glycines on soybeans in Illinois in 2000 and its potential control,” (1 Feb. 2001 available at the “plantmanagementnetwork” org website). It rapidly spread throughout the region and into other parts of North America (Patterson, J. and Ragsdale, D., “Assessing and managing risk from soybean aphids in the North Central States,” (11 Apr. 2002) available at the planthealth.info website in subdirectory soyaphid and further subdirectory aphid02. High aphid populations can reduce crop production directly when their feeding causes severe damage such as stunting, leaf distortion, and reduced pod set (Sun, Z. et al., “Study on the uses of aphid-resistant character in wild soybean. I. Aphid-resistance performance of F2 generation from crosses between cultivated and wild soybeans,” (1990) Soybean Genet. News. 17:43-48). Yield losses attributed to the aphid in some fields in Minnesota during 2001, where several thousand aphids occurred on individual soybean plants, were >50% (Ostlie, K., “Managing soybean aphid,” 2 Oct. 2002) available at the soybeans University of Minnesota website under successive subdirectories crop, insects, aphid, aphid_publication_managingsba with an average loss of 101 to 202 kg ha−1 in those fields (Patterson and Ragsdale, supra). In earlier reports from China, soybean yields were reduced up to 52% when there was an average of about 220 aphids per plant (Wang, X. B. et al., “A study on the damage and economic threshold of the soybean aphid at the seedling stage,” (1994) Plant Prot. (China) 20:12-13) and plant height was decreased by about 210 mm after severe aphid infestation (Wang, X. B. et al., “Study on the effects of the population dynamics of soybean aphid (Aphis glycines) on both growth and yield of soybean,” (1996) Soybean Sci. 15:243-247). An additional threat posed by the aphid is its ability to transmit certain plant viruses to soybean such as Alfalfa mosaic virus, Soybean dwarf virus, and Soybean mosaic virus (Sama, S. et al., “Varietal screening for resistance to the aphid, Aphis glycines, in soybean,” (1974) Research Reports 1968-1974, pp. 171-172; Iwaki, M. et al., “A persistent aphid borne virus of soybean, Indonesian Soybean dwarf virus transmitted by Aphis glycines,” (1980) Plant Dis. 64:1027-1030; Hartman, G. L. et al., supra; Hill, J. H. et al., “First report of transmission of Soybean mosaic virus and Alfalfa mosaic virus by Aphis glycines in the New World,” (2001) Plant Dis. 561; Clark, A. J. and Perry, K. L., “Transmissibility of field isolates of soybean viruses by Aphis glycines,” (2002) Plant Dis. 86:1219-1222).
Because A. glycines is a recent pest in the USA, a comprehensive integrated management approach to control the aphid has yet to be developed. Research to evaluate the efficacy of currently-available insecticides and other control measures has just begun.
An integral component of an integrated pest management (IPM) program to control aphids is plant resistance (Auclair, J. L., “Host plant resistance,” pp. 225-265 In P. Harrewijn (ed.) Aphids: Their biology, natural enemies, and control, Vol. C., Elsevier, New York (1989); Harrewijn, P. and Minks, A. K., “Integrated aphid management: General aspects,” pp. 267-272, In A. K. Minks and P. Harrewijn (ed.) Aphids: Their biology, natural enemies, and control, Vol. C., Elsevier, New York (1989). Insect resistance can significantly reduce input costs for producers (Luginbill, J. P., “Developing resistant plants—The ideal method of controlling insects,” (1969) USDA, ARS. Prod. Res. Rep. 111, USGPO, Washington, D.C. Resistance was reported in G. soja (Sun, Z. et al., “Study on the uses of aphid-resistant character in wild soybean. I. Aphid-resistance performance of F2 generation from crosses between cultivated and wild soybeans,” (1990) Soybean Genet. News 17:43-48), a close relative of G. max (Hymowitz, T., “On the domestication of the soybean,” (1970) Econ. Bot. 24:408-421), and other wild relatives (Zhuang, B. et al., “A study on resistance to soybean mosaic virus and Aphis glycines of perennial wild soybean,” (1996) Soybean Genet. Newsl. 23:66-69). Prior to 2004, there were no reports of resistance in G. max. A report from Indonesia had indicated that there was no resistance in a test of 201 soybean cultivars and breeding lines (Sama, S. et al. (1974) Research Reports 1968-1974, p. 171-172. In Varietal screening for resistance to the aphid, Aphis glycines, in soybean. Agricultural Cooperation, Indonesia, the Netherlands).
There are numerous examples of the discovery and use of resistance genes to control aphids in crops other than soybean. Examples include Russian wheat aphid (Du Toit, F. (1987), “Resistance in wheat (Triticum aestivum) to Diuraphis noxia (Homoptera:Aphididae),” Cereal Res. Commun. 15:175-179; wheat greenbug (Tyler, J. M., et al. (1985), “Biotype E greenbug resistance in wheat streak mosaic virus-resistant wheat germplasm lines,” Crop Science 25:686-688), potato aphid on tomato (Kaloshian, I., et al. (1997), “The impact of Meu-1-mediated resistance in tomato on longevity, fecundity and behavior of the potato aphid,” Macrosiphum euphorbiae,” Entomol. Exp. Appl. 83:181-187), and cotton-melon aphid on melon (Klinger, J. et al. (2001), “Mapping of cotton-melon aphid resistance in melon,” J. Am. Soc. Hortic. Ci. 136:56-63).
A number of soybean markers have been mapped and linkage groups created, as described in Cregan, P. B., et al., “An Integrated Genetic Linkage Map of the Soybean Genome” (1999) Crop Science 39:1464-1490.
U.S. Patent Publication 2006/0014964, Hill, C. B., et al. (2006), “Soybean aphid resistance in soybean Jackson is controlled by a single dominant gene,” Crop Science 46:1606-1608, and Hill, C. B., et al. (2006), “A single dominant gene for resistance to the soybean aphid in the soybean cultivar Dowling,” Crop Science 46:1601-1605 disclose two previously-discovered soybean aphid resistance genes, Rag1 in Dowling and another gene in Jackson.
A trait that maps to soybean Linkage Group F is root-knot nematode resistance. (Tamulonis, J. P., et al. (1997), “DNA marker analysis of loci conferring resistance to peanut root-knot nematode in soybean,” Theor. Appl. Genet. 95:664-670.) Jeong, S. C. et al., “Cloning And Characterization Of An Rga Family From The Soybean Molecular Linkage Group F,” in an Abstract published by Plant & Animal Genome VIII Conference, Town & Country Hotel, San Diego, Calif., Jan. 9-12, 2000 at a website address with the usual www prefix followed by intl-pag.org/8/abstracts/pag8255.html and in Yong G. Yu, Glenn R. Buss, and M. A. Saghai Maroof (1996), “Isolation of a superfamily of candidate disease-resistance genes in soybean based on a conserved nucleotide-binding site,” PNAS, 93:11751-11756, discloses that the soybean chromosomal region on linkage group F flanked by the markers K644 and B212 contains several virus, bacteria, fungus and nematode resistance genes.
Conventional plant breeding for insect resistance traditionally relied on screening whole plants for resistance directly with live insects and assessing insect population development or plant damage caused by insect feeding, or indirectly with techniques that measure insect feeding behavior, such as Electrical Penetration Graph (EPG). Implementation of these techniques requires a certain amount of time and specialized space, such as in a greenhouse or plant growth room. More efficient and cost-effective molecular genetic and polymerase chain reaction (PCR) techniques, with the development of DNA markers, enable breeders to significantly increase throughput and efficiency in screening plants for traits that are tightly linked to DNA markers, by screening genomic DNA of plants in the laboratory. There are numerous examples of the use of this technology to select plants with certain traits in breeding programs, including insect resistance. Other publications directed to marker-identification of soybean aphid resistance include Li, Y, et al., “Soybean aphid resistance genes in the soybean cultivars Dowling and Jackson map to linkage group M,” Molecular Breeding (in press); Hill, C. B., et al. (2006), “Soybean aphid resistance in soybean Jackson is controlled by a single dominant gene,” Crop Science 46:1606-1608; Hill, C. B., et al. (2006), “A single dominant gene for resistance to the soybean aphid in the soybean cultivar Dowling,” Crop Science 46:1601-1605; Li, Y., et al. (2004) “Effect of three resistant soybean genotypes on the fecundity, mortality, and maturation of soybean aphid (Homoptera:Aphididae),” Journal of Economic Entomology 97:1106-1111; Hill, C. B., et al. (2004) “Resistance to the soybean aphid in soybean germplasm and other legumes,” p. 179, World Soybean Research Conference, Foz do Iguassu, PR, Brazil; Hill, C. B., et al. (2004), “Resistance to the soybean aphid in soybean germplasm,” Crop Science 44:98-106; and Hill, C. B., et al. (2004), “Resistance of Glycine species and various cultivated legumes to the soybean aphid (Homoptera:Aphididae),” Journal of Economic Entomology 97:1071-1077). Additional methods and molecular tools are needed to allow breeding of A. glycines resistance into high-yielding G. max soybean varieties.
All publications referred to herein are incorporated herein by reference to the extent not inconsistent herewith.